drm/i915: Remove BXT restore arbitration around ctx switch

This w/a (WaDisableCtxRestoreArbitration) was only used for preproduction
hw, which is no longer in use. Remove the workaround to simplify the code.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170123130601.2281-3-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_lrc.c

@@ -1102,10 +1102,6 @@ static int gen9_init_indirectctx_bb(struct intel_engine_cs *engine,
 	struct drm_i915_private *dev_priv = engine->i915;
 	uint32_t index = wa_ctx_start(wa_ctx, *offset, CACHELINE_DWORDS);
 
-	/* WaDisableCtxRestoreArbitration:bxt */
-	if (IS_BXT_REVID(dev_priv, 0, BXT_REVID_A1))
-		wa_ctx_emit(batch, index, MI_ARB_ON_OFF | MI_ARB_DISABLE);
-
 	/* WaFlushCoherentL3CacheLinesAtContextSwitch:skl,bxt */
 	ret = gen8_emit_flush_coherentl3_wa(engine, batch, index);
 	if (ret < 0)
@@ -1202,10 +1198,6 @@ static int gen9_init_perctx_bb(struct intel_engine_cs *engine,
 		wa_ctx_emit(batch, index, MI_NOOP);
 	}
 
-	/* WaDisableCtxRestoreArbitration:bxt */
-	if (IS_BXT_REVID(engine->i915, 0, BXT_REVID_A1))
-		wa_ctx_emit(batch, index, MI_ARB_ON_OFF | MI_ARB_ENABLE);
-
 	wa_ctx_emit(batch, index, MI_BATCH_BUFFER_END);
 
 	return wa_ctx_end(wa_ctx, *offset = index, 1);